Process for the preparation of monochromates and dichromates



CE? PROCESS ron THE PREPARATloN F t MONOOHBOMATES A D: DVICHROMATVES I. :meSEmisnai-a, c sarmaamnce, as l signer to Bd'zel-Maletra,SocitIndustrielle de 7 a I a i I Produits Chimiques, Paris, l lrance a c j z ai tion of France a 1, in; Drawing. ,xppisafioiiivia'y; "25, 1933, Serial No. 72,904. 'In France MayZG, 1932 *8 Claims. (ems-c) I The present invention relates tothe manufacture of monochromates and dichromates.

In my prior Patent No. 1,955,326, dated April 1-7, 1934,,1 have described and claimed a process for manufacturing, monochromates anddichromates with oxidizing ferro-chrome or a substance containing metallic chromium, as starting ma 'terials, in the presence of waterand an alkaline agent by means of an oxidizing gas underpressure; lhave already proposed to prepare monochromates by subjecting at temperatures above 100 C., chromium hydroxide, hydrated chromium oxide, chromium oxide or chrome ore, or substances containing .the same, to an oxidizing decomposition in the presence of alkaline: or alkaby subjecting at temperatures above 100'C.;chromium hydroxide, hydrated chromium oxide, chro- V mium oxide orsubstancescontaining the same or chrome ore, to an. oxidizing decomposition inthe presence of alkaline-' or alkaline earth hydroxides, carbonates or .bicarbonates or monochromate's'in an aqueous medium, the quantity of alkaline agent employed being such that it remains below that required for the formationfof monochromates.

In accordancewith'the present invention-ithas been 'found that for .thev formation of nionochromates orrdichromates, theipresence of alkalineor alkalineearth hydroxides, carbonates or bicarbonates or of monochromates is not abso'r lutely necessary. rAccording'to the invention it is possible to employlin'stead of ortogether with these alkalineor alkaline earth agents and in the case of the'preparation of dichromates instead ofor together with alkaline-or alkaline earth agents or monochromates, in general all compoundscapable of yielding their alkaline prin-.'

ciple underioxidizing conditions in the course of the process. 1

an oxygen-yielding? reagenttlike, potassium "chlorate; U

The tendency ofchromium, to be converted into hexavalent chromium-is so markedithat-inthe course of the'oxidation-fprocess the'substance's added undergo a splitting-'-up :which; causes them ions (cations) .fjf-

um. ,a qor'dina to, the quantity of the alkaline xprinciple entering into reaction it isfpossible to to igiveupjtheir alkalineprinciple tothe chromi In ordento 'proper1y;. distinguish between an .falkaline agent?.per seand a substance which in this- .case' underproper oxidizing conditions will it is well to remember that:

A solution of an acid contains :hydrogenions (cationsland non-metallic ions (anions) -j.a solution of" a base contains hydr'oxyl ions (anions) and metallic 'ions (cations); and a solution ofa alt "contains nonrmeta-llic (anions) andfmetallic an acid thefanions are the active elements which combine witlrthe attacked metal, forming chlorides, sulphates, phosphates, nitrates, etc.-,'

freeing" the hydrogen. In a base or alkaline ,agentiit is the cation'which isthe active 'element, while-in aisalt solution the anions and cations bind and'neutrali'ze each Otheryas long as no decomposition"takesplacei Onlywhn and after such decomposition is efiected under' special circumstances, free acting cations are liberated and a: chemical reaction isrealized. Thus a substance which" normally cannot be classified as base, can become an alkalineagent'.

While an'alka'line agent contains its-cation in afiree state," the substances employed according toj the present' inventionsare those capable of liberatingth'eirjcations generally under the oxiidi'zing 'actioncf the reaction. V Ido not claim as lily-present invention the use of .oxides, hydroxides of: alkali or alkali earth metals" taken alone. Nor do Iclaim the use of carbonates of alkalior alkaliearth metals taken alone. Neither do I claim as'qa part of my'presentinvention the use of monochromates per se as "a substance capable of giving up free 'a'ctingications to the substance containing chromium oxide under the influence a of the Ioxidizing reaction.

As compounds which in themselves are not bases, but in s the presence of an -'oxidizing reac- "tionare capable of, giving up their alkaline principle to jthechromium it is possible to em'ploy "the most varied saltsof strong or weakinorganic F or organic acids oralsooxygen"containingicompounds of a salt like character for example alkalineor alkaline earth sulphates, 'chlori'des,"'ph'osphatsac'etates, monochromates, silicates, aluminates, nitrates, chlorates, per-salts, manganates,

permanganates' and; thei -like. It may be rej marked that these latter 'compoundsjcan act at If for example organic derivatives are employed the organic principle is ingeneraloxidized to carbon dioxide which can conveniently be elimi-' 1 nated during the operation. Certain compounds capable of giving up their alkaline principle can be used alone, while in the case of certain others it is to be recommended that they should be used in conjunction with substances acting as neutralizing agents as for example the oxides or carbon ates of the alkaline earths. By way of example which is in no way limiting of the present process the following examples are given and it may be remarked that Example 1 illustrates the splitting upof sodium sulphate under-the action of the oxidizing decomposition of trivalent chromium. r I I As a matterof fact, the salts-just indicated above are not basesbut are capable of giving up their cations under the action of the oxidizing reaction. Said characteristic is clearly exemplified by the following Examples 1, 2, 7, and 8.

Examples (1) 9.38 parts of'hydrated chromium oxide (containing 81% of CrzO3),--7.1,partsof anhydrous sodium sulphate and 200 parts of water are heated to 280-290 C. for 6 hoursin a stirring autoclave. Before commencing the heating of the apparatus it is filled with oxygen under 15 atmospheres. I

By removing the contents of the'apparatus it is found that a large part of the hydrated chromium oxide is converted into sodium bichromate together with free mineral acid.

The yield is 22.16%. The concentration of the sulphuric acid in the solution is about 0.5%. It may be remarked that the reaction does not progress beyond a decomposition corresponding to about 0.5% H2504.

avoid exceeding this limiting acidity.

( 9.38 parts of hydrated chromium, oxide (containing 81% of Cr203), 7.1 parts of sodium sulphate, 5 parts of calcium carbonate and 200 parts of water are heated to 280290 C. for about 10-15 hours in the presence of oxygen under 15 atmospheres in a stirring autoclave.

After cooling a bichromate liquoris withdrawn from the apparatus leaving a residue consisting for the mostipart of calcium sulphate.

The yield is -97% bichromate.

(3) 9.38 parts of hydrated chromium ox ide (containing 81% of CrzOs), 17.42partsofcrystallized trisodium phosphate (10"mo1ecules .of water) and 225 parts of-waterare heated to 280-290 C. for about 9 hours in thepresence of oxygen under 15 atmospheres in a stirringautoclave. i r r Sodium bichromate and mono-sodium phosphate are formed according to the reaction;

V Na2C r20'I+NaI I2PO4.

The yield of bichromate is 93.3%. l If instead of trisodium phosphate an equiva lent quantity of disodium phosphate is employed The yield can be considerably increased by a further dilution in order to the same time as oxidizing agents and when de- 1 composed as alkaline agents.

the oxidation likewise takes place with good yield.

(4) 9.38 parts of hydrated chromium oxide (containing 81% of CrzOz) 11.73 parts of sodium silicate (containing 34.1% or sodium hydroxide) and 225 parts of water are-heated to 280-290 C. for about 9 hours under 15 atmospheres of oxygen ina stirring autoclave.

The product obtained is a solution of bichromate'with a residue of silicic acid. .The yield is .'95.3,% of sodium bichromate.

(5 9.38. parts of hydrated chromium oxide i (containing 81% of CI'zOs), 10.11 parts of potassium nitrate, 5 parts of calcium carbonate and 225 parts ofwater are heated to 280-290 C. for about10-15 hours under 15 atmospheres of oxygen in a stirring autoclave.

The product obtained is potassium bichromate together with calcium nitrate. The yield'of hexavalent chromium is 90%. V v a (6) 9.38 parts of hydrated chromium oxide (containing 81%of Cr2O3), 12.25 parts of potassium chlorate, 5 parts of calcium carbonate and 200 parts of water are-heated at 280-290" C. for about 10-15 hours and'without the presence of oxygen in a stirring autoclave. The reaction is as follows: 1

After cooling there is found in the apparatus free oxygen under pressure. The yield of bi- 'chromate is about8890%.

If double the quantity of hydrated chromium oxide-and an equivalent quantity of alkali are employed the oxygen formed will serve for the conversion of this additional quantity of hydrated chromium oxide according to the reaction 7) 9.38 parts of hydrated-chromium oxide conthan that of the vapour tension.

Whenthe reaction is complete the residue of calcium sulphate is filtered and the monochromate-is separated by known means. The yield is practicallyquantitative; Instead of calcium car- "bonate it is likewise possible:v toemploy caustic lime. I

(8) 7.6 parts of chromimn oxide 90-95%.(11'203, 14.5 parts of anhydrous sodium sulphate, 10 parts of calcium carbonate, 200 parts of water, are heated for about 15 hours with good agitation in an autoclave to BOO-350 C. A current of oxygen or.v air under pressure is caused to pass through. The progress of the reaction can be followed by the content of carbonic acid of the gas escaping from the apparatus.

At the end of the reaction residual calcium sulphateis filtered and the monochromateobtained in anexcellent yield is separated by any known *means." vJ

(9) 9.38 parts of hydrated chromium oxide,

81% C12O3,'-'7O parts'of trisodium phoshate 10 Aq., 225 parts of water are heated in an atmosphere of oxygen or in a current of air under. pressure for 10-15 hours at -300? C. V

The product of the reaction is composed of a liquorcontainingsodium nionochromate and disodium phosphate; yield 90-95%.

' reaction.

. under pressure and in an aqueous medium, in the presence of a substance beingnot normally classified as base, but other than a monochromateand (10) 9.5 parts of hydrated chromium oxide of CrzOs, 24.5 parts of potassium chlorate, 4.19 parts of magnesium oxide of 96.3% MgO, 200 parts of water are heated for 10-15 hours at 290-300 C.

At the end of thereaction free oxygen under pressure is present in the apparatus.

The productof the reaction is filtered from a small quantity of magnesia andchromium substance which are not attacked.

The potassium chromate obtained is separated by crystallization. I v

Oxidation yield 80-90%.

I claim:

1. Process for the manufacture of monochromates or dichromates consisting in subjecting a substance containing chromium oxide to oxidizing decomposition at temperatures above C. un-

der pressure and in an aqueous medium, in the presence of a substance being not normally classiffied as base,.but other than a monochromate and capable of giving up free acting cations to the chromium under the influence ofthe oxidizing 2.;Processfor the manufacture of monochromates or dichromates consisting in subjecting a substance containing chromium oxide to oxidizing decomposition at temperatures above 100C. un-

.der pressure and in an aqueous medium, in the a presence of a substance being not normally classified as base, but other than a monochromate and capable of giving up free acting cations tothe chromium under the influence of the oxidizing re action and in the presence of an alkaline agent.

3. Process for the manufacture of monochromates or dichromates consisting in subjecting a substance containing chromium oxide to oxidizing decomposition at temperatures above 100 C. un-.;

der pressure and in an aqueous medium, inthe presence of a substance being not normally classified as base, but other than a monochromate and capable of giving up free acting cations to the chromium under the influence of the oxidizing re action, andacting at the same time as oxidizing agent.

4. Process for the manufacture of monochro I mates or dichromates consisting in subjecting a substance containing chromium oxide to oxidizing decomposition at temperatures above 100 C.

capable of giving upfree acting cations to the chromium under the influence of the oxidizing reaction and acting at the same time as oxidizing agent, and inthe presence of an alkaline agent.

5. Process for the manufacture of monochromates or dichromatesconsisting in subjecting chrome ore to oxidizing decomposition at temperatures above 100 C. under pressure and in an aqueous medium, in the presence of a substance being not normally classified as base, but other than a monochromateand'oapable of giving up free acting cations tothe chromium under the influence of theoxidizing'reaction. V

6. Process for the manufacture of monochromates and dichromates consisting in subjecting chrome ore to oxidizing decomposition at temperatures above 100 C. under pressure and in an aqueous medium, in the presence of a substance being not normally classified as base, but other than a monochromate'and capable of giving up free acting cations to the chromium under themfluence of the oxidizing reaction, and in the presence of an alkaline agent.

7. Process for the manufacture of monochroperatures above 100 C. under pressure and in an aqueous medium, in the presence of a substance beingnot normally classified as base, but other than a monochromate and capable of givingup 'free'acting cations to the chromium under the in-. I fluence of the oxidizing reaction and acting at the same time as oxidizing agent, and in the presence of an alkaline agent. 7 I

1 JULES. EMILE DEMAN'I'. 

